By pausing audio during flash writes, the worst screeching of #8121
is avoided. I don't consider this a full fix, but it greatly improves
the by far most common scenario in which the problem occurs.
Tested on rp2040 prop feather with a midi synth playing arpeggios. When
writing to the flash e.g., with
```
dd bs=512 count=32 if=/dev/zero of=/media/jepler/CIRCUITPY/boop
```
the audio goes "tap tap tap tap" during the flash write instead of the
squawking.
This isn't a 100% fix; it will still glitch out, including during USB
enumeration which must be taking a long time without servicing background
tasks. Add a delay if not usb-connected at startup ameliorates this
greatly.
PicoDVI in CP support 640x480 and 800x480 on Feather DVI, Pico and
Pico W. 1 and 2 bit grayscale are full resolution. 8 and 16 bit
color are half resolution.
Memory layout is modified to give the top most 4k of ram to the
second core. Its MPU is used to prevent flash access after startup.
The port saved word is moved to a watchdog scratch register so that
it doesn't get overwritten by other things in RAM.
Right align status bar and scroll area. This normally gives a few
pixels of padding on the left hand side and improves the odds it is
readable in a case. Fixes#7562
Fixes c stack checking. The length was correct but the top was being
set to the current stack pointer instead of the correct top.
Fixes#7643
This makes Bitmap subscr raise IndexError instead of ValueError
when the index arguments are wrong.
Now a 'once' and a 'loop' buffer can be specified.
'once' is useful for things like writing a neopixel strip in the background,
if you can guarantee the buffer contents are stable until the write is complete.
'loop' is useful for periodic things, like pwm & servos.
both together are useful for some special cases of pwm/servo, where a
transitional waveform needs to be played for one repetition and then
a new waveform needs to be played after that.
The API is renamed to reflect that it's a more generic 'background'
operation.
RP2040 and SAMD51:
- Detect when DMA has finished, and stop DMA audio explicitly.
- Do not accidentally reuse `first_buffer` supplied by WaveFile or RawSample. Always realloc `first_buffer` and `second_buffer`
RP2040:
- When audio playing is stopped, write a final zero to the output register. This prevents residual PWM tones.
- Handle buffer size for 8-bit samples properly for 16-bit output.
- Fail on some edge cases (which may not be possible at the moment).
1. Check for correct error values from dma_claim_unused_channel.
2. Introduce a .stereo flag for simplicity.
3. Clarify PWM carrier frequency choice.
4. Start introducing quiescent audio value. Still need to ramp up/down.
5. Redo audio stop logic a bit.
6. Fix (unrelated) displayio dependency things.
There is still an interference problem between other DMA users and audio. Still debugging this.
This adds I2SOut and PDMIn support via PIO.
StateMachines can now:
* read and read while writing
* transfer in 1, 2 or 4 byte increments
* init pins based on expected defaults automatically
* be stopped and restarted
* rxfifo can be cleared and rxstalls detected (good for tracking when
the reading code isn't keeping up)
Fixes#4162
